If the frame is stamped with the same 118xxx number, then what you may have is a factory mash-up. Tony Curzon would be the one to help you out with this anomaly.
As I understand it, when AMC went bankrupt in 1966, Manganese Bronze bought Norton (they already owned Villiers). They were enticed to also take Matchless, but let that company whither and die.
Berliner wanted scramblers, both P11 and N15, so the factory did what they could to fill orders, sometimes re-stamping engine cases. If you talk to Mike Partridge of Walridge Motors, He'll tell you about 2 N15s he has with re-stamped engine cases where one could just make out '33' under the N15. The factory had converted some AJS 33s to N15 spec and shipped them out. The Factory also sold a few CSRs (both Matchless and AJS) as Atlas 750SS.
Your bike falls into that time period when shortcuts were taken to fill orders.
My G15 is titled as a G15 and is stamped as such. However, it came with one Norton tank badge (no title), so may have originally sold as a Norton. Again, from the end of that same time period.